Three children were fighting for their lives after a sudden spring storm sent a bolt of lightning crashing down on a birthday party in a Paris park.
A spokesman for Paris' fire service credited an off-duty firefighter with playing a critical role in getting medical help to the victims.
The birthday group in Paris had sought shelter under a tree at Parc Monceau, an area popular with families, when a lightning bolt touched down, according to Paris fire service spokesman Eric Moulin.
He said Pascal Gremillet, an off-duty firefighter, was visiting a museum nearby when he noticed the commotion and found nine of the 11 victims lying unconscious. He immediately went to work.
"He saw who was the most seriously injured. He did a quick triage of the victims. He did first aid. He alerted the rescue services," Moulin said. "Without his actions, it would have been much worse."
Moulin said six of those hit were seriously injured, with three children and one adult fighting for their lives. He said five others had been slightly injured by the lightning, including four children.
Footage shot by the fire service showed a dramatic scene at a nearby bank that was commandeered as a makeshift treatment centre, with children wrapped in gold thermal blankets sitting and lying on the building's tiled floor as firefighters administered first aid before evacuating the victims to hospitals.
Two small feet, smudged with what looked like soot, stuck out from underneath one of the blankets.
Moulin gave the children's ages as around nine.
An Associated Press reporter at the scene saw an abandoned pair of children's glasses and jacket near the tree. White-and-red tape was strung around the area and whistle-blowing park wardens ushered weekend joggers out of the park, which was swiftly closed.
"This accident is extremely rare in the Paris region," professor Pierre Carli, an emergency medical services official, told reporters.
One Paris resident who lives near the park and saw the lightning crash down said it was rare to see such a wild storm hitting the French capital.
"It was dramatic," said Jean-Louis Laurens.